1. Field of the Invention
The present invention relates to an automatic assembling method, and more particularly to a method of automatically assembling a photographic film cassette, or the like, and an apparatus for practicing the method.
2. Description of the Related Art
Photographic film of the 135 type, contained in a cassette, as among the most popular formats of photographic film. A known 135 photographic film cassette has a cassette shell constituted of a cylindrical body formed of a thin metal sheet and two caps fitted thereon. The cassette shell has a spool contained therein on which photographic film is wound in a form of a roll. To assemble this photographic film cassette, several methods are known. For example, U.S. Pat. No. 4,614,019 (corresponding to Japanese Patent Publication No. 2-691) discloses a process of winding the photographic film on the spool, and then assembling the cassette in a darkroom: U.S. Pat. No. 4,080,711 (corresponding to Japanese Patent Publication No. 60-48748) discloses a process of bringing the assembled cassette shell into the darkroom, disassembling the cassette shell for insertion of the photographic film, inserting the photographic film wound on the spool, and then assembling the cassette shell.
U.S. Pat. No. 4,834,306, U.S. Pat. No. 4,846,418 and European Publication EP-A2 0 406 815 (corresponding to Japanese Patent Laid-open Publication No. 3-37645), each disclose a photographic film cassette in which a cassette shell is constituted of parts formed from resin, and rotation of a spool causes a leader of the photographic film to exit to the outside of the cassette. Such a leader-advancing cassette is different from conventional photographic film cassettes because the leader of the photographic film is fully contained within the cassette both before exposure and after exposure. Such a cassette is advantageous in that the photographic film is reliably protected from accidental exposure to ambient light, and in that the cassette is easily handled.
Such a leader-advancing cassette includes elements not utilized in conventional cassettes. As disclosed, for example, in U.S. Pat. No. 4,834,306 (corresponding to Japanese Patent Laid-open Publication No. 1-306845) and U.S. Pat. No. 5,049,912, a light-shielding shutter member may be mounted openably in a photographic film passage port of this type of film cassette for protecting the inside from ambient light. Or a visual indicator member may be incorporated in such a cassette, to appear externally for indicating the exposed condition of the photographic film. However, production of such a leader-advancing cassette has many inherent problems due to the increase in the number of the parts. Particularly when the cassette shells must be assembled or disassembled in a darkroom, the assembling operation is so complicated that production efficiency is difficult to increase. In such a case, even an automated assembling machine does not reliably increase production efficiency.
The problems are more complicated for a photographic film cassette wherein a spool is an assembly constituted of a pair of flanges force-fitted of the spool core, and the spool assembly is mounted in one shell half before the other shell half is joined therewith. This is because an independent assembling process for assembling the spool assembly is necessary before a primary assembling process of the film cassette, wherein the spool assembly, the shutter plate and other parts are mounted into the cassette. In such a case, there are at least two assembling lines and at least a transfer conveyor for connecting the two lines. Therefore, the mechanism of the conventional system are complicated. The need for transferring works between the lines increases the occurrence of problems. The same problem as described above could generally arise in other automatic assembling systems, where a secondary assembly should be incorporated into a primary assembly.
On the other hand, a constant tact intermittent transport linear base machine for moving an endless conveyor member such as a belt or a chain periodically by a constant amount, is known, for example, from Japanese Patent Laid-open Publication 4-209121, wherein pallets are secured to the endless conveyor member. When assembling works by using such a constant tact intermittent transport linear base machine, if positions of the pallets get out of order because of jamming of the works, stop positions of the pallets must be readjusted to restore the accuracy of assemblage. Readjustment requires a great deal of time so that the efficiency of the assembly process decreases.
Conventional constant tact intermittent linear base machines further have a problem in that the pallet must be decoupled from and coupled to the conveyor to be fed back to the assembling line, through a feed back line, after the completion of assemblage on that pallet. The decoupling-coupling operations often cause problems especially in a high speed tact system.
In view of the above problems, an object of the present invention is to provide an automatic assembling method, and an apparatus for that method, which enables a high efficiency assembly operation, even when a secondary assembly must be assembled into a primary assembly in a primary assembling process, while the secondary assembly is assembled in an independent secondary assembling process.
Another object is to provide an automatic assembling apparatus which uses a constant tact intermittent transport linear base machine, but eliminates deviation of pallets and trouble in decoupling and coupling of the pallet being conveyed at short intervals.
A further object of the present invention is to provide an automatic assembling method for assembling a cassette shell of a film cassette inclusive of a spool assembly in a single assembling line.
To achieve the above and other objects, according to the present invention, each of a plurality of integrally formed pallets has a secondary work holder and a primary work holder which are arranged in the same desired positions. Parts of a secondary assembly are sequentially fed to the secondary work holder and are assembled into the secondary assembly in the secondary work holder in each pallet during conveying the pallets. The secondary assembly and other parts of a primary assembly are sequentially fed to the primary work holder and are assembled into the primary assembly in the primary work holder in each pallet during conveying the pallets.
Therefore, it is unnecessary to provide a secondary assembling line for assembling the secondary assembly separately from a primary assembling line for the primary assembly. Because of the single assembling line, it is unnecessary to provide interconnecting devices such as a synchronizing device and a buffer conveyor, which would otherwise be necessary for connecting the primary and secondary assembling lines.